Fix adapter aliasing for single-cell RNA-seq (fixes #8)

[v0pluto]

Summary

• Add adapter lookup normalization (lowercase/trim, spaces-hyphens to _, collapse repeated _)
• Add alias mapping for single-cell RNA-seq variants to canonical adapter key
• Preserve ValueError for unknown adapters

Canonical key

• transcriptomics_single_cell

Test

• .venv/bin/pytest -q tests/unit/core/test_adapter_aliases_issue8.py